1. Field of the Invention
The present invention relates to a hydraulic valve head clearance eliminating device, that is called hydraulic lash adjustor, in a valve operating mechanism and more particularly to an improved hydraulic lash adjustor for automatically eliminating valve head clearance in the valve operating mechanism for an internal combustion engine with the aid of resilient force given by a resilient means and hydraulic force so that the valve operating mechanism can be reliably and quietly operated for a long period of time and excellent durability is assured.
2. Description of the Prior Art
In general, a hydraulic lash adjustor is equipped with a check valve located in the interior thereof so as to open or close a hydraulic passage formed in the adjustor and due to the fact that the check valve moves violently within a valve cage which serves to contain the valve therein there is necessity for firmly holding the valve cage in order to assure that the check valve operates properly at all time.
To facilitate understanding of the present invention it will be helpful that a hitherto known hydraulic lash adjustor will be described below with reference to FIGS. 1 and 2. The hydraulic lash adjustor includes a cylinder 1 which serves as a housing therefor. As is apparent from the drawings, the cylinder 1 is designed in the form of a bottomed hollow cylinder which is open at upper end part 1a while having a closed bottom wall 1b at the lower end part thereof and which is fitted into a support hole Ea of an engine casing E. A plunger 2 with a semi-spherical top part 2a formed at its upper end is slidably inserted into the cylinder 1 through the open end part 1a and a hydraulic chamber 3 is defined between the lower end part of the plunger 2 and the bottom wall 1b of the cylinder 1. Further, the plunger 2 is formed with a hydraulic oil reservoir chamber 4 in the interior and has a valve bore 5 at its bottom portion by way of which bore the hydraulic oil reservoir chamber 4 is in communication with the hydraulic chamber 3. The hydraulic oil reservoir chamber 4 is in communication with a hydraulic oil supply passage 10 via a through hole 6 on the side wall of the plunger 2, an annular hydraulic passage 7 between both the sliding surfaces of the cylinder 1 and the plunger 2, a through hole 8 on the side wall of the cylinder 1 and an annular hydraulic passage 9 on the outer surface of the cylinder 1 so that the chamber 4 is always filled with hydraulic oil which is delivered through the hydraulic oil supply passage 10.
The plunger 2 includes a cylindrical portion 11 at its lower end which is adapted to abut against a shoulder 1c formed on the inner side wall of the cylinder 1 at a position located in the proximity of the bottom of the latter so as to define a positional limit of downward movement of the plunger 2.
A valve cage 12 is disposed in the hydraulic chamber 3. Specifically, the valve cage 12 comprises a main body 12a and a flange portion 12b made integral with the former and extending radially outward from the upper end of the body 12a. A through hole 13 is formed on the side wall of the main body 12a and the outer peripheral part of the flange portion 12b is fitted into an annular engagement groove 14 on the inner side wall of the cylindrical portion 11 of the plunger 2.
A check valve 15 in the form of a ball is floatably housed in the valve cage 12 so as to open or close the valve bore 5. The conventional hydraulic lash adjustor is so constructed that the check valve 15 is caused to open as hydraulic pressure in the hydraulic chamber 3 decreases and close as it increases and a stopper 16 is provided at the bottom of the valve cage 12 so as to confine a working stroke of the check valve 15. Further, to assure that the plunger 2 projects upward above the upper end of the cylinder 1 a resilient spring 17 in the form of a coil spring is contained in the hydraulic chamber 3 to apply thrusting force to the plunger 2 from the bottom side thereof.
The semi-spherical top end part 2a of the plunger 2 abuts against the righthand end part of a rocker arm R as seen in FIG. 1 and the lefthand end part of the latter abuts against the valve head of a poppet valve V which serves to open or close an intake valve or an exhaust valve on the engine casing E, wherein an operating cam C is disposed at a position intermediate between both the righthand and lefthand end parts of the rocker arm R so that the poppet valve V is opened by rotation of the operating cam C. The poppet valve V is usually equipped with a valve spring S in the form of a coil spring which is adapted to urge the valve in the closing direction. It should be noted that resilient force of the valve spring S is set far stronger than that of the resilient spring 17 in the hydraulic chamber 3.
Next, operation of the conventional hydraulic lash adjustor will be described below.
While the poppet valve V is kept closed, the plunger 2 is caused to move upward under the influence of resilient force of the resilient spring 17 until the righthand end part of the rocker arm R is raised up and thereby clearance between the lefthand end part of the rocker arm R and the valve head of the poppet valve V is eliminated. As the plunger 2 is raised up and thereby hydraulic pressure in the hydraulic chamber 3 decreases, the check valve 15 is opened and hydraulic oil in the hydraulic oil reservoir chamber 4 flows into the hydraulic chamber 3 via the valve bore 5 whereby the hydraulic chamber 3 is filled with hydraulic oil again.
Next, when the cam face on the operating cam C comes in contact with the rocker arm R as it is rotated, the rocker arm R is depressed its intermediate part and thereby valve opening force is generated. In response to valve opening force, hydraulic pressure is developed in the hydraulic chamber 3 which has been kept closed by means of the check valve 15 and it results that the plunger 2 is supported under application of the thus developed hydraulic pressure onto the bottom surface thereof. Thus, the rocker arm R is caused to pivot downwardly toward the poppet valve V about the semi-spherical end part 2a of the plunger 2 which serves as a fulcrum, whereby the poppet valve V is opened against resilient force of the valve spring S. During the downward pivoting movement of the rocker arm R, a very small amount of hydraulic oil in the hydraulic chamber 3 leaks through close clearance between the sliding surfaces of the cylinder 1 and the plunger 2 but the leaked amount of hydraulic oil will be compensated by an auxiliary supply from the hydraulic oil reservoir chamber 4 during next closing operation of the poppet valve V.
However, it has been found that a conventional hydraulic lash adjustor of the above type has the following drawbacks because of the fact that the valve cage 12 with the check valve 15 housed therein is held in place merely by fitting its flange portion 12b into the annular engagement groove 14 on the inner side wall of the cylindrical portion 11 of the plunger 2.
(1) There is fear of causing disconnection of the valve cage 12 from the annular engagement groove 14 when a considerably large volume of air enters the hydraulic chamber 3 during operation of an engine at a high speed or oil feeding, because the check valve 15 resonates in the valve cage 12 and a high intensity of impulsive force caused by such resonance is adversely transmitted to the valve cage 12.
(2) To inhibit disconnection of the valve cage 12 in that way there has been proposed an arrangement that interferencial dimension is provided for the flange portion 12b of the valve cage 12 so as to allow it to be forcibly fitted into the annular engagement groove 14. The valve cage 12 is generally manufactured by press forming, because a machining operation causes a substantially increased manufacturing cost. To practice the proposal there is necessity for maintaining dimensional tolerance of the flange portion 12b of the valve cage 12 within a strictly close range but it is difficult to meet this necessity so that interferencial dimension fluctuates. If the interferencial dimension is excessively small, there is fear of causing the valve cage 12 to drop out of its place in the same manner as in the foregoing. On the contrary, if it is excessively large, plastic deformation tends to take place with the flange portion 12b at the time of fitting into the annular engagement groove 14, resulting in an occurance of fluctuation in clearance for displacement of the check valve 15 within the valve cage 12. Furthermore, there may be a case where it becomes difficult to assure an extent of displacement of the check valve 15 required for its intended operation. In another case, there may be produced a cracking in the valve cage 12, resulting in that the valve cage 12 becomes liable to drop out of its place in the annular engagement groove 14.
(3) To assure that the flange portion 12b of the valve cage 12 is reliably fitted into the annular engagement groove 14 it is inevitably necessary to keep an appreciable amount of dimensional clearance between the width of the annular engagement groove 14 and the thickness of the flange portion 12b of the valve cage 12. However, this in turn causes the valve cage 12 to move toward and away from the plunger 2 or to rotate in the groove 14 and moreover unpleasant noise is generated due to abutment or frictional sliding movement of the former with respect to the latter. Thus, it becomes impossible to keep constant the extent or displacement of the check valve. Also in this case there is fear of causing the check valve to drop out in the above-described manner.